Safety helmet



A. G. GROSS Aug. 14, 1956 SAFETY HELMET 2 Sheets-Sheet 1 Filed Feb. 18, 1954 A- G. GROSS SAFETY HELMET Aug. 14, 1956 2 Sheefs-Sheet 2 Filed Feb. 18, 1954 INVEN TOR.

firm/e G. 6/3055 SAFETY HELMET Arthur G. Gross, Torrance, 'Calif., assignor to Protection Inc., Inglewood, Calif, a corporation of California Application February 18, 1954, Serial No. 411,163,

2 Claims. (Cl. 23)

This invention relates to safety helmets of the type worn by construction workers, auto-racing drivers, and

edge,- a scientific, methodical approach to the designing In the past, such helmets of crash or safety helmets. have generally comprised a hard shell incorporating suspension straps adapted to rest on the wearers head. A suitable space between the inner dome surface of the shell and" the top of the Wearers head is maintained by these straps. This space will permit movement of the outer shell under an impact and thus prevent the dome frame striking the wearers head provided the energy ofthe impact does not exceed the energy absorbable by the supporting straps and the dome structure. The energy thatmay be absorbed by the helmet is a function of thereferred to spacing between the head straddling portions of the straps and the shell, and the resiliency or tensioncharacteristics of the supporting straps.

In some prior art approaches to the design of a helmet for properly absorbing the energy of blows received thereby, there has been incorporated in the straps themselves or between the straps and the shell some type of elastic or resilient material that will give in the man net of a spring, following fairly closely Hookes law. The product of the integrated force exerted by such'material and the distance through which such force acts defines the absorbable energy. The available distance through which such integrated force can act inthe case of the helmet is the distance between the straps and the shell. Any increased movement beyond such available distance will result in the impact being communicated to the Wearers head with consequent injury.

Because of the elastic properties of the straps or compression materials, the initial energy absorption is rela tively small and precious space is used up. As the elastic materials stretch or are compressed, however, the forces increase and more energy is absorbed as the remaining available space is used. As a result of this distribution of the energy spectrum, a force of sufiicient magnitude to fracture a persons skull or break his neck may be reached before sufficient energy from the impact has been absorbed. This force at which serious injury to the head will result is referred to hereinafter as the threshold force.

It is evident from the above, that best potential protection will be afiorded by a helmet which is designed to absorb all the energy of the impact before forces in the helmet strap structure exceed the threshold force.

Generally, any impact received by a helmet will fall between two extreme conditions, to wit: (a) impact by a large blunt mass of relatively low velocity, and (b) impact of a small penetrating mass of high velocity.

2,758,305 a en e Au 1 1 56 The design of a suitable protective helmet must take into accountthese. two conditions. In the first case of impact by a large mass of relatively lowvelocity,.little, change in velocity of the impacting body will occur due to the relative masses. Forces set upin the helmet and supporting strap structure therefore resultpredomin'antly from acceleration of thewearers head andb'ody resulting from the impact. Under these conditions, the primary function of the helmet is to permit acceleration of: the headand'body from the path of the impacting body. without the setting up of forces greater than therreferr e'd to threshold force. It is to be noted that any local deformation of the dome or shellportion'ofthe. helmet relative to the head and straps at a force appreciably'bee. low the threshold force will result in the using up of some of the available space for-energy'absorptiodand may, therefore, be considered as'a loss of the'maximum potential protective performance of the helmet; Accord ingly, thefirst step in the design of the helmet is the. provision of anextremely rigid shell whereby substane tially no local indentationsoccur butrather all forces are-communicated to-the supporting straps.

In the second case of impact by a smallmass of high velocity, it is assumed that the totalforce on the head at no time exceeds the threshold force. The function-of the supporting straps under these conditions then, is to, maintain the maximum available spacing; or 'distance. be'-. tween the head andshell whereby if partialpenetratiqil of the mass through the shell'occurs, the: chances offthe' body contacting the head are minimized. Any. displacef ment of the shell relative to the head underforces less tha n thethreshold force may thus alsobeconsid'eredf ailoss the maximum potential protective performance er the helmet; I

In each extreme case, and in intermediate conditions, it is seen that best protection is realized'when the helmet is constructed to absorb a maximum amountv of energy within the available space. With such an arrangement, there is greatly decreased the possibility of the threshold force being exceeded during normally contemplatedi'ni-l pacts.

Bearing the above principles in mind, the primary. object of the present invention is the provision iof'a'safety. helmet incorporating energy absorbingmeans of novel construction whereby the helmet structure can absorb considerably more energy without exceeding a given threshold force and within a given ,available's'pacing -bea tween the wearers head and the helmetshelhthan has heretofore been possible.

Briefly, this object is realized by avoiding the usezof. elasticor resilient energy absorbing materials, andsub stituting in lieu thereof elements or. materials which will yield only when a given force is attained. This given force is calculated to have a magnitude slightly lessthan thethreshold force in order to provide. a safety. margin but inasmuch as it is substantially constant, its: action: through a given distance results in maximumenergy. ab,- sorption within said distance. v i

The theory and principles underlying the invention, as well as some preferred embodiments. thereof, will be better understood by referring to the. accompanyingdrawings in which: I

Fig. 1 is a schematic diagramof one. type ofknown helmet;

Fig. 2 is a graph illustrating the: energy. absorbing characteristics of the helmet of Fig. l; i

Fig. 3 is a schematic drawingof a helmet constructed in, accordance withthe present invention;

Fig. 4 is a graph illustrating the energy absorbing; characteristics of the-helmet of Fig.3; VI

Fig; 5 is an elevational cross-section view of a preferred helmetconstruction in accordance with the invention;

Fig. 6 illustrates in cross-section a plan view of the helmet of Fig.

Fig. 7 is an enlarged elevational view of one type of energy absorbing means employed in the helmet of Fig. 5;

Fig. 8 illustrates a modified type of energy absorbing means which may be substituted for the element shown in Fig. 7;

Fig. 9 shows how the device of Fig. 8 appears atfer it has yielded or absorbed energy;

Fig. 10 illustrates a third embodiment of the energy absorbing means in exploded view;

Fig. 11 is a cross-section taken along the line 11-11 of Fig. 10; and,

' Fig. l2vis another view of the device of Fig. 10 useful in explaining its operation.

Referring now to Fig. 1, there is shown a conventional helmet comprising a hard dome or shell 10 and a suspensiouor supporting strap 11. Strap 11 is secured in any suitable manner to the inside periphery of the helmet brim in a manner to leave a given spacing X0 between the head-straddling portion thereof and the shell 10. This distance X0 is hereinafter referred to as the available distance or spacing.

In most prior art safety helmets, the energy of an impact is absorbed by a stretching of the supporting straps. This stretching is accommodated by the distance X0. In some instances, elastic material is incorporated in the straps themselves or between the straps and the shell. In any case, the giving of the straps under impact is essentially an elastic phenomenon in which Hookes law is followed reasonably closely. In Fig. 1, this elastic characteristic, however achieved, is symbolically represented by the small springs 12.

Fig. 2 is a graph of force vs. distance, the force scale being represented by the ordinate axis F and the distance through which the force acts being represented by the abscissa axis X. The curve 13 represents the variation of force due to impact on the shell 10 of the helmet with the distance between the shell and the wearers head. This curve, for the sake of simplicity in illustrating the underlying theories of the invention, is shown as a straight line, as would be the case if Hookes law were followed exactly. In reality, the curve for a conventional helmet would start with a more gradual slope and increase in slope at the upper end, being more or less concave in shape.

The available distance is designated on the abscissa scale in Fig. 2 as X0. It will be noted that since curve 13 is shown for convenience as essentially rectilinear, the slope thereof is equal to the net spring constants of the springs 12. It will be immediately evident that the shaded area under curve 13 between the limits 0 and X0 repreisents1 the maximum absorbable energy by the helmet of Now if F0 represents the threshold force or force at which the wearers skull will fracture or neck be broken, it will be evident that, for an impact whose total energy is represented by the shaded area in Fig. 2, the force in the straps and thus imparted to the wearers head will exceed the threshold force F0 at the point X1. This distance X1 is less than the available distance X0 and therefore the available distance has not been employed to maximum advantage. The proportion of energy absorbed by the helmet before the threshold force is reached is given by the area under curve 13 between the limits 0 and X1. The present invention is primarily concerned, therefore, with increasing the amount of energy that can be absorbed before the threshold force is reached.

This increase in the absorbing property or protection potential of the helmet is accomplished as follows: Referring to Fig. 3, instead of springs 12, there is incorporated in the straps an energy absorbing means in the form of yieldable elements 14. These elements are constructed to yield only when a certain predetermined force has been attained, and then to yield uniformly under a substantially constant force.

As shown in Fig. 4, this predetermined force is designated F1 and is adjusted to a magnitude slightly less than the threshold force F0. Under these circumstances, there will be be no appreciable stretch in the straps until the force F1 is attained, at which time, the straps will yield uniformly until the available distance X0 is used up. This characteristic is represented by the curve 15 of Fig. 4. It will be noted that there is an initial slope to this curve. This slope is greatly under-exaggerated for purposes of clarity; it represents the initial elastic properties of all materials which when subjected to a force will give in accordance with Hookes law until the elastic limit is reached at which time they yield. Actually, the level portion of the curve 15 for some materials may have a slight slope, since, even in yield, some materials will exhibit some elastic properties. This slight slope is of negligible importance, however.

From an examination of the shaded area under curve 15, it will be seen at once that considerably more energy is absorbed within the distance X1 as compared to Fig. 2, and that at no time, is the threshold force exceeded. Thus, the helmet of Fig. 3 could absorb the total energy of the impact without exceeding the threshold force F0 of Fig. 2, the energy defined by the area of the triangle T being absorbed within the area under the curve 15 of Fig. 4 between the limits 0 and X1. This additional ability to absorb energy is the direct result of the yielding characteristics of the energy absorbing means 14. As stated, these elements do not operate in accordance with Hookes law but are designed to operate beyond. the elastic limit and thus yield, resulting in a plastic deformation thereof. The yielding which takes place under a constant force of predetermined magnitude results in the level characteristic of the curve 15. It is this energy absorbing characteristic as depicted in the graph of Fig. 4 which distinguishes the present invention from all prior art shock absorbing means incorporated in safety helmets.

Figs. 5 and 6 illustrate a preferred form of energy absorbing means and the manner of incorporating the same in the strap supporting portions of a helmet. As shown, the preferred type of helmet comprises straps 21,v 22, and 23. These straps each have their opposite ends secured to one end of a yieldable element 24, the other end of the yieldable element being secured to the inside of the helmet brim as at 25. A conventional type sweat band or padding 25a covers the connections 25 to provide a comfortable cushioning against the sides of the wearers head.

Each of the energy elements 24 are identical and description of one will suifice for all. Referring to Fig. 7, the element 24 is shown as comprising a tab or plate 26 having slotted opening 27 to which the end of one of the straps such as 22 is secured. The other end of the element 24 comprises a tab or plate 28 secured to the helmet brim at 25. Between plates 26 and 28 there are secured a plurality of helically wound steel wires 29. The windings are such that there is little if any elasticity in the helical windings, but their number and the diameter of the coils may be adjusted to vary the force at which these wires will plastically deform under tension. Thus, the predetermined force at which the ele-' ment 24 will yield can be accurately adjusted by the number and proper dimensioning of the wire coils. As stated, this force is adjusted to a value slightly less than the threshold force to provide a safety margin. In practice, the ratio of the outside diameter of the helical coil to the wire diameter is made as small as possible-and with maximum pre-loading so that the coil will immediately begin to yield when the proper force is attained.

In operation, when an impact is received by the helmet shell 20 of Fig. 5, the forces of the impact will be borne by the straps until the predetermined force F1 is reached. During this period very little, if any, of the available space X will be used up. When the force F1 is reached, however, the wires will yield under this force uniformly and they will thus absorb energy as they stretch through the available distance. This absorption will be the maximum amount capable of being absorbed without exceeding the threshold force as indicated by the level or straight line characteristic of the curve 15 as explained above.

Fig. 8 illustrates another type of energy absorbing element which may be substituted for the coiled wires 29 of Fig. 7. In this latter embodiment there is provided a metal strip of a given thickness depending upon the predetermined force F1. Into the edges of this strip there are provided a series of cuts 31. Centrally of the strip there are provided additional cuts 32. The lengths of these cuts can be varied to vary the force at which the strip will yield.

Under action of an impact force, the strip 30 of Fig. 8 will yield only when a predetermined force has been attained. This plastic deformation or yielding results in the configuration illustrated in Fig. 9 which shows the strip after it has absorbed energy. The stretching force results in the cuts 31 and 32 separating to form V gaps 33 and diamond-shaped openings 34 respectively. It is to be emphasized, that once the predetermined force has been attained the deformation continues under a constant force.

Figs. to 12 illustrate yet another means of obtaining an energy absorbing characteristic as depicted in Fig. 4. In this embodiment, there is provided a channel element 35 adapted to be secured to the inside brim portion of the helmet as by fastenings 36. Channel 35 has its longitudinal edges 37 and 38 turned over to oppose one another to form a longitudinal slot 39 of narrower width than the channel. The suspension or supporting strap 22 of the helmet is secured to a button plate 40 from which there extends a shaft 41 having an enlarged head 42. The shaft 41 has a diameter slightly larger than the width of the slot 39, while the head 42 is dimensioned to ride within the channel of member 35 all as clearly shown in Figs. 11 and 12.

The end side portions of the walls 37 and 38 may be enlarged as at 43 and 44 (Fig. 10) to permit the button plate 40 to be initially snapped into position and thus secured to the helmet brim.

When an impact force is set up in the supporting straps due to an impact on the shell of the helmet, the button plate 40 is pulled upwardly. The enlarged head 42 rides within the channel of the member 35 and guides this motion. Because of the fact that the diameter of the shaft portion 41 is larger than the slot 39, the shaft will peel back the walls 37 and 38 as it rides upwardly.

The force necessary to effect this peeling is adjusted by making the walls of a specified strength and thickness, to equal the predetermined force desired. This force will be constant as the bottom plate moves along the channel and thusa force-distance characteristic curve as shown in Fig. 4 is realized.

An advantage of the particular arrangement shown in Figs. 10 to 12 resides in the fact that the initial slope of the force-distance curve is exceedingly steep since there is essentially negligible elastic action in the mechanism.

It will be understood, of course, that all of the yieldable elements described are expendible and once they have absorbed energy a new element must be inserted in their stead.

It is also to be understood that the principles of energy absorption set forth above have application to other safety devices besides helmets such as safety belts employed by scaffolding workers. In any instance then, where it is desired to absorb a maximum amount of energy within a given spacing without exceeding a given threshold force, the principles of the present invention are applicable.

I claim:

1. A safety device comprising: a helmet having a substantially rigid shell, suspension means secured to the shell and adapted to rest on a wearers head and space the top of the wearers head a given clearance distance from the interior surface of the shell, and a metal coil interposed in said suspension means to provide yieldability therein, the diameter of said wire and the diameter of said coil having values such that said coil exhibits elastic elongation substantially according to Hookes law through a maximum distance materially less than said given clearance distance when subjected to a given tensional force and plastically elongates at substantially constant force in a range within the balance of said clearance distance when subjected to a tensional force greater than said given force.

2. The subject matter of claim 1, wherein a plurality of the metal coils as defined are arranged in parallel in said suspension means.

References Cited in the file of this patent UNITED STATES PATENTS 712,016 Stern et al. Oct. 28, 1902 1,251,537 Kempny Jan. 1, 1918 1,416,866 Patterson May 23, 1922 2,159,681 Wisman May 23, 1939 2,585,937 Johnson et al Feb. 19, 1952 FOREIGN PATENTS 864,280 France Apr. 23, 1941 

